Well at least you have a purpose for doing them. Like others said I would be careful with the behind the neck stuff especially with how heavy you are going. Shoulder and lower back injuries can be chronic and fuck you up bad in the long term

better off doing snatches from your knees, or at the very least using a hammer strength jammer.

...well, based strictly on the video evidence presented to getbig in recent times, I don't think Steve is on his knees to get to anyone's snatch, if one wishes to speculate as to the video's true target market. However, I think we can all say that Steve is in fact successfully "jamming his hammer with strength", as you put it above. It might be more of akin to needlenose plyers rather than a hammer, but your point is not lost on us.

Advices? First you make an video which proves that you can't understand anything about training, and then you ask for advice? I have one for you: The one and only thing which you have to do the effect while training, is the muscle group which you are training. Not the pencilnecks in the gym, not your ego, not your friends. Only the fucking muscle. Simply enough? What you do there, is show off, because you think that you have done something special. What you have accomplish, is make a fool of yourself.